Networking › Module 5 › Lesson 3
Lab — Diagnose a Broken Connection
Walk through a structured troubleshooting scenario step by step
Opening
Scenario: "The site won't load"
A user reports: "I can browse some sites but https://cyberlium.com times out." You will not reboot blindly—you will test each layer and record evidence. Follow the steps even if your network is healthy; the commands are what matter in a real ticket.
1. Step 1 — Confirm Local Stack
Local stack checkping -c 3 127.0.0.1 ip a
ping -c 3 127.0.0.1 ip a
Expect loopback replies and an UP interface with an inet address. If this fails, fix the host before blaming the internet.
2. Step 2 — Reach the Gateway and Internet by IP
Gateway and public IP testip route | grep default ping -c 3 <your-gateway-ip> ping -c 3 8.8.8.8
ip route | grep default ping -c 3 <your-gateway-ip> ping -c 3 8.8.8.8
Note which hop fails. Gateway failure = LAN issue. Gateway OK but 8.8.8.8 fails = routing or ISP.
3. Step 3 — Test DNS
DNS resolution testdig cyberlium.com +short nslookup cyberlium.com dig @8.8.8.8 cyberlium.com
dig cyberlium.com +short nslookup cyberlium.com dig @8.8.8.8 cyberlium.com
You should get one or more A record IPs. Empty answer, SERVFAIL, or timeout implicates DNS servers or filtering.
4. Step 4 — Test the Application (HTTP/S)
HTTPS verbose connection testcurl -v --connect-timeout 10 https://cyberlium.com
curl -v --connect-timeout 10 https://cyberlium.com
Read the output: Connected to ... port 443 — TCP and TLS path works. Could not resolve host — DNS problem. Connection timed out — firewall, routing, or service down. SSL certificate problem — trust or proxy issue, not basic connectivity.
5. Step 5 — Write the Diagnosis
Symptom
What the user reported in one sentence.
Tests run
ping, dig, curl results with pass/fail.
Likely layer
Link, IP, gateway, DNS, or application.
Complete Broken Connection Lab
Run all five steps against cyberlium.com (or another HTTPS site). Save a short report in ~/cyberlium-lab/connection-diagnosis.txt with each command, its result, and your conclusion. If everything works, note "all layers healthy" and which test would fail in each failure mode.